Relation between the pelvis and the sagittal profile in adolescent idiopathic scoliosis: the influence of curve type.

Previous studies have shown a correlation between pelvic parameters and the lumbar lordosis in normal subjects and in scoliotic adults. This study investigates the relationship between pelvic and spinal geometries in the sagittal plane for adolescent idiopathic scoliosis (AIS) patients having various curve types. The study group was composed of 129 AIS patients classified according to their curve type: King I, King II, King III or lumbar curve. The SpineView software (Surgiview, France) was used to compute five parameters on sagittal x-rays: thoracic kyphosis (TK), lumbar lordosis (LL), sacral slope (SS), pelvic tilt (PT) and pelvic incidence (PI). The TK was significantly lower for King I, II and III curves as compared to the lumbar curves. The LL tended to be higher for patients having a major lumbar scoliotic (King I and lumbar) curve, although not significantly. No significant change between the groups was observed for the SS, PT and PI. The PI was significantly correlated to the LL, SS and PT for all groups. The SS was strongly related to the LL in all cases. However, no relationship was found between the TK and the LL in any group. This study showed that the TK mostly depends on the thoracic scoliotic curve and therefore on the shape and orientation of the vertebrae, which explains that many King I, II and III patients are hypokyphotic. Conversely, the LL is mainly influenced by the pelvic configuration. Since the pelvic parameters are similar for all groups, these parameters are not likely to be important in the development of a specific type of scoliotic curve.